Asymmetric Synthesis of 1,2,3-Substituted Cyclopropanes

Significance

The established approaches to 1,2,3-substituted cyclopropanes usually involve the formation of the preactivated ring followed by introduction of the third substituent. The recent work of Charette and co-workers (J. Am. Chem. Soc. 2009, 131, 15624) describes a highly enantio-selective method based on this concept. Herein, this group reports a direct approach, representing the first enantioselective cyclopropanation of al­kenes by zinc carbenoids generated in situ from diazo compounds. A number of products was ­obtained with a wide range of yields (42-98%), good to excellent enantioselectivities (86-99% ee) and dr values up to >95:5. In addition, the first Simmons-Smith reaction using a catalytic amount of zinc salt is reported, which furnished 2 with 95% yield and a dr of 4:1.